Release Of Trace Elements Research Articles

RESEARCH ON RELEASE OF TRACE ELEMENTS AT RETORTING OF HUADIAN OIL SHALE

Oil shale is abundant in the world. Today, the industry of oil shale retorting for producing shale oil is developing owing to high price of crude oil in the world. In order to study migratory behavior of trace elements in oil shale at retorting, tests were performed in laboratory with oil shale of the Huadian deposit of China at different temperatures from 360 to 560 °C. Trace elements Ba, Co, Cr, Cu, Mn, Ni, P, Pb, Sr, Ti, V, Y present in oil shale and shale char were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Hg and As were determined by atomic fluorescence spectroscopy (AFS). By comparing the content of trace elements in oil shale and shale char, distribution characteristics of trace elements at retorting were studied. The analysis of trace elements indicates that in comparison with the earth crust averages, oil shale samples are richer in some elements, including Mn (more than 30×), P (more than 6×), and Ti (more than 5×). The amounts of Ti, Ba, Co, Cr, Cu, Mn, and V are increased in shale char at retorting. Pb and Hg start to volatilize at 410 °C. Shale char is enriched with arsenic by about 50% at temperatures from 360 °C to 560 °C. Reducing atmosphere promotes the release of trace elements. The effect of heating rate on different elements was also studied in these experiments. For most of the elements, their release from oil shale can be promoted by higher heating rate and nitrogen atmosphere.

Leaching of ashes from co-combustion of sewage sludge and wood—Part I: Recovery of phosphorus

Combustion of sewage sludge with subsequent recovery of phosphorus is a relatively new sludge treatment option. In the work described in this paper, recovery of phosphorus by acid leaching of fly ashes from co-combustion of sewage sludge with wood in a circulating fluidized bed combustor was investigated. The results showed that it is possible to find a pH range (0.5–1) in which one can extract a significant fraction of the phosphorus from these ashes without precipitation of secondary phosphates. The type of flocculation agent used in the waste water treatment plant where the sludge is formed has a significant effect on the phosphorus recovery. Ashes from combustion of sewage sludge that was formed using aluminium sulphate as flocculating agent released nearly all phosphorus at a pH value of 1. When iron sulphate was used as flocculating agent, this affected the chemistry of the resulting ashes, making phosphorus recovery more difficult. The yield of phosphorus from those ashes was 50–80%. In Part II of the project [Pettersson et al. Leaching of ashes from co-combustion of sewage sludge and wood. Part II: The mobility of metals during phosphorus extraction. Biomass and Bioenergy 2007 in press, doi:10.1016/j.biombioe.2007.09.006 [1].] focus is on the trace element release to the leachate. This determines if the leachate can be used directly as a fertilizer or if further removal of trace elements is necessary.

The Double Solid Reactant Method for modeling the release of trace elements from dissolving solid phases: I. Outline and limitations

A Double Solid Reactant Method was elaborated from a suggestion of Marini (Geological sequestration of carbon dioxide: Thermodynamics, kinetics, and reaction path modeling. Developments in Geochemistry, Elsevier, Amsterdam, 2007) to simulate the release of trace elements during the progressive dissolution of solid phases. The method is based on the definition, for each dissolving solid, of both an entity whose thermodynamic and kinetic properties are known (either a pure mineral or a solid mixture) and a special reactant, that is, a material of known stoichiometry and unknown thermodynamic and kinetic properties. The special reactant is utilised to take into account the concentrations of trace elements in the dissolving solid phase. In this communication, the influence of several trace elements on the ΔG f o, ΔG r o and log K of the minerals considered by Lelli et al. (Environ Geol, 2007) and Accornero and Marini (Geobasi, 2007a; Proceedings of IMWA symposium, Cagliari, 27–31 May 2007b) was evaluated assuming ideal mixing in the solid state. These effects were found to be negligible for albite and the leucite–latitic glass, limited for muscovites and chlorites, and slightly more important for apatites. These influences become progressively higher with increasing concentration of trace elements in these minerals. Based on these deviations in thermodynamic parameters, special reactants should not include oxide components with molar fractions higher than 0.003.

The Determination of Trace Elements Release from Dental Cements in Artificial Saliva by Energy Dispersive X‐ray Fluorescence Spectrometry

The application of energy dispersive X‐ray fluorescent analysis (EDXRF) for the determination of elements released from five different dental luting cements such as Zinc Polycarboxylate (Carbchem), Zinc carboxylate (Adhesor Carbofine), Glass ionomer (Meron), Resin cement (Duo‐cement kit), and Carboxylate (Durelon) in artificial saliva is described. The equipment used for this study is a Si(Li) detector, a multichanel analyser, an amplifier and 55Fe and 241Am radioisotope sources. The physical basis of the analytical method used the procedure of sample preparation and results are presented. The detected elements were Cl, P, K, Ca. The results show high concentrations of Ca being released from dental cements in artificial saliva. Chemical disintegration of dental cements can adversely affect their long‐term performance. Fixed prosthodontic restorations cemented with carboxylate cement (Durelon) may be capable of withstanding long‐term clinical use compared to other agents. This material showed the highest resistance to dissolution or disintegration.

Fate of trace elements during alteration of uraninite in a hydrothermal vein-type U-deposit from Marshall Pass, Colorado, USA

Alteration of uraninite from a hydrothermal vein-type U-deposit in Marshall Pass, Colorado, has been examined by electron microprobe analysis in order to investigate the release and migration of trace elements W, As, Mo, Zr, Pb, Ba, Ce, Y, Ca, Ti, P, Th, Fe, Si, Al, during alteration, under both reducing and oxidizing conditions. The release of trace elements from uraninite is used to establish constraints on the release of fission product elements from the UO 2 in spent nuclear fuels. Uraninite occurs with two different textures: (1) colloform uraninite and (2) fine-grained uraninite. The colloform uraninite contains 1.04–1.75 wt% of WO 3, 0.16–1.70 wt% of As 2O 3, 0.06–0.88 wt% of MoO 3; whereas, the fine-grained uraninite retains 2.25–4.93 wt% of WO 3, up to 5.76 wt% of MoO 3, and 0.26–0.60 wt% of As 2O 3. The near constant concentration of incompatible W in the colloform uraninite suggests W-incorporation into the uraninite structure or homogeneous distribution of W-rich nano-domains. Incorporation of W and Mo into the uraninite and subsequent precipitation of uranyl phases bearing these elements are critically important to understanding the release and migration of Cs during the corrosion of spent nuclear fuel, as there is a strong affinity of Cs with W and Mo. Zoning in the colloform texture is attributed to variation in the amount of impurities in uraninite. For unaltered zones, the calculated amount of oxygen ranges from 2.08 to 2.32 [apfu, (atom per formula unit)] and defines the stoichiometry as UO 2+ x and U 4O 9; whereas, for the altered zones of the colloform texture, the oxygen content is 2.37–2.48 [apfu], which is probably due to the inclusion of secondary uranyl phases, mainly schoepite. The supergene alteration resulted in precipitation of secondary uranyl minerals at the expense of uraninite. Four stages of colloform uraninite alteration are proposed: (i) formation of an oxidized layer at the rim, (ii) corrosion of the oxidized layer, (iii) precipitation of U 6+-phases with well-defined cleavage, and (iv) fracture of the uraninite surface along the cleavage planes of the U 6+-phases.

Leaching experiments to study the release of trace elements from mineral separates from Chinese coals

Leaching experiments were carried out for two samples of mineral separates from Chinese coals for the purpose to simulate the release of trace elements in acid mine drainage. The leaching solution has a ferric ion concentration of 10 − 3 M, pH ≈ 2. The experiments were carried out at room temperature. The grain size of the mineral separates is 75–130μm. The behavior of the release of eight trace elements (Co, Ni, Zn, Cd, Al, Cr, As, and Pb) were measured during the period of 312h. The results from four leaching tests using two samples with two solid-to-liquid ratios show that the concentrations of Co, Ni, Zn, and Cd continuously increased during the leaching period and they were correlated with the sulfate content in the same leachate. This indicates that the elements were released during the oxidation and dissolution of pyrite. The elements were easily dissolved in the leaching solution. On the other hand, the concentrations of Al, Cr, As, and Pb in the leachates varied considerably under same leaching conditions and were sensitive to the condition of the leachate during the leaching process. The release of these four elements was affected by the pH of the leachate and by absorption and co-precipitation. They are less likely to migrate. Therefore, the release and migration of the eight elements in acid coal-mine drainage are controlled mainly by three factors, the oxidation of pyrite, the pH of the leachate, and mineralogy of country rocks.

An experimental study of dissolution kinetics of Calcite, Dolomite, Leucogranite and Gneiss in buffered solutions at temperature 25 and 5°C

Laboratory experiments were carried out continuously for 30–35 days at 25 and 5°C in three different buffer solutions of pH 4.0, 2.2 and 8.4 to calculate dissolution rates of two minerals, calcite (CC) and dolomite (DM) and two rocks, leucogranite (LG) and gneiss (GN) from the Himalayan range. Calculated rates in terms of release of targeted elements versus time (Ca for CC; Mg for DM; Si for LG and GN) demonstrate direct correlation with temperature. Dissolution rates are higher at 25°C compared to 5°C. CC and DM were experimented only at pH 8.4 and results show that both undergo congruent dissolution with CC dissolving ∼5 times faster than DM. Ca and Mg exhibit average apparent activation energies (E a) of 13.98 and 9.98 kcal mol−1 respectively at pH 8.4 which reflects greater sensitivity of CC dissolution than DM dissolution towards an increase in temperature. Scanning Electron Microscope attached with Energy Dispersive X-Ray Analyser (SEM-EDX) data indicates that dissolution is controlled primarily by surface-reaction processes, with dislocation sites contributing maximum to the dissolution. As compared to CC and DM dissolution, LG and GN undergo relatively slower incongruent dissolution with precipitation of some secondary minerals as revealed from X-ray diffractometer (XRD) results. Rates of dissolution of LG is maximum at pH 2.2, moderate at pH 8.4 and least at pH 4.0, whereas GN shows maximum dissolution at pH 2.2, moderate at pH 4.0 and least at pH 8.4. A comparison in dissolution behavior of LG and GN at experimental conditions reveals that increase in Si-release rate in the temperature range between 5 and 25°C is maximum at pH 8.4 (∼3.4–4.5 times), moderate at pH 4.0 (∼3–1.8 times) and least at pH 2.2 (∼1.0–1.5 times). Within the experimental temperature range, calculated values of E a for Si release during LG and GN dissolution advocates positive correlation with pH. A substantial decrease in initial values of Brunauer–Emmett–Teller (BET) surface area of DM, LG, and GN has been encountered at the end of the experiment, except for CC for which an increase is observed. The study clearly demonstrates the dissolution behavior of pure minerals and rocks under controlled conditions. The dissolution rates assume enormous significance for the release of trace elements from rocks/minerals to the reacting water.

Study on the fate of As, Hg and Pb in Yima coal via sub-critical water extraction

Arsenic, lead and mercury are the major hazardous trace elements contained in coals. During coal combustion these trace elements release and emit to the atmosphere and cause harmful effects to the human beings and the environment. This paper is to study the fate of arsenic, lead and mercury in Chinese Yima coal by sub-critical water treatment. The experiments were performed in a semi-continuous apparatus. Demineralization, float-sink experiment and sequential chemical extraction were carried out in order to examine the transformation of occurrence mode of the three elements. The results show that with increasing temperature and residence time, the removal of As, Pb and Hg increases. At 410 °C, 15 MPa, 30 min, with water flow rate of 450 ml/h, the removal of mercury and arsenic is about 100% and 57%, respectively. It is difficult to remove lead by sub-critical water extraction. Arsenic and lead in Yima coal are associated not only with pyrite, but also with monosulfides and sulfates, other minerals including silicates, aluminum silicates etc. and organic matters. Mercury is mainly associated with pyrite (about 75%) by adsorption, and is also associated with other minerals such as clays, silicates, aluminum silicates etc. During sub-critical water treatment, arsenic associated with carbonates, sulfates and monosulfide, pyrite and other minerals all decrease, and that associated with organic matters increase. Only a little lead in Yima coal is removed by this process. Mercury associated with pyrite and other minerals decreases, and that associated with sulfates and monosulfides disappears after sub-critical water extraction.

Health Impacts of Coal: Facts and Fallacies

Coal has contributed enormously to the advance of civilization by providing an abundant, inexpensive, and convenient source of energy. Concurrent with its contributions, coal has extracted a high cost in terms of environmental damage and human health impacts. Coal will remain a key component of the global energy mix for decades to come as well as a major source of global pollutants. Despite its high media profile, misconceptions about coal abound, especially with regard to its human health impacts. Coal also provides several excellent examples of how a geologic material and human health intersect in a variety of surprising ways. Unfortunately, the links between coal use and human health are distorted by a great deal of ignorance and misinformation. This paper discusses the facts and fallacies of the direct health impacts caused by coal (1, 2). There are a number of important health issues caused by coal that fall outside the scope of this review. The health impacts of particulates emitted from coal combustion have received substantial attention since the groundbreaking work of Wilson et al. (3), and through the recent discussions by Davis (4) and Freese (5). The indirect health impacts of coals through their contributions to global climate change, respirable particulates, acid rain, and acid mine drainage are also beyond the scope of this review. Greb et al. provide an excellent general overview of the environmental impacts of coal (6). The potential for health impacts caused by exposure to trace elements has received considerable attention for the past quarter of a century. The US Environmental Protection Agency conducted an extensive study of this issue and concluded (7) that, with the possible exception of mercury, there was no compelling evidence of health impacts caused by the emission of trace elements from coal-burning electric generating utilities. Nevertheless, documented examples do exist of health impacts caused by trace elements emitted by coal combustion. Bencko and Symon (8) described hearing problems in children living near a power plant burning high arsenic coal in the former Czechoslovakia. But, perhaps the most significant example of health impacts caused by trace element release from coal use occurs in Guizhou Province, southwest China, where millions of people suffer from dental and skeletal fluorosis and thousands suffer from arsenic poisoning due to mobilization of these elements by burning mineralized coals in unvented or poorly vented stoves (Figs. 1a and b).

Interpretation of standard leaching test BS EN 12457-2: is your sample hazardous or inert?

A slag sample from a lead refiner has been obtained and given to two analytical laboratories to determine the release of trace elements from the sample according to BS EN 12457-2. Samples analysed by one laboratory passed waste acceptance criteria, leading it to be classified as an inert material; samples of the same material analysed by the other laboratory failed waste acceptance criteria and were classified as hazardous. It was found that the sample preparation procedure is the critical step in the leaching analysis and that the effects of particle size on leachability should be taken into account when using this standard. The purpose of this paper is to open a debate on designing a better defined standard leaching test and making current waste acceptance criteria more flexible.

Squeezing out the slab — modelling the release of Li, Be and B during progressive high-pressure metamorphism

A model for the release of Li, Be and B from progressively dehydrating altered oceanic crust during subduction is presented. Combining clinopyroxene/fluid partition coefficients determined experimentally in an earlier study Brenan et al. [Brenan, J.M., Ryerson, F.J., Shaw, H.F., 1998. The role of aqueous fluids in the slab-to-mantle transfer of boron, beryllium, and lithium during subduction: Experiments and models. Geochim. Cosmochim. Acta 62, 3337–3347] with apparent mineral/clinopyroxene partition coefficients as observed in natural high-pressure metamorphic rocks Marschall et al. [Marschall, H.R., Altherr, R., Ludwig, T., Kalt, A., Gméling, K., Kasztovszky, Zs., 2006a. Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks. Geochim. Cosmochim. Acta 70, 4750–4769] results in a set of mineral/fluid partition coefficients for high-pressure metamorphic minerals. Mineral modes of altered oceanic crust as a function of pressure and temperature along a given subduction path can be derived from thermodynamic calculations using the program PerpleX. Combination of these modes with mineral/fluid partition coefficients results in whole rock/fluid partition coefficients at any stage of the P– T path including information on the amount of fluid released at any depth. Based on these data, the concentrations of Li, Be and B in subducting rocks and released fluids along a given P– T path can be modelled. The derived information on B concentrations in rocks and fluids are combined with the temperature-dependent fractionation of B isotopes in order to model the B isotopic evolution of subducting rocks and released fluids. Model calculations are performed for two slightly different chemical compositions (hydrous MORB without K and with 0.5 wt.% K 2O), in order to demonstrate the impact of phengite on the boron budget. Provided the necessary input data are available, the concept of such a model could be employed to quantify the trace element release from the slab from any lithology along any reasonable P– T path.

Aqueous fluids and hydrous melts in high-pressure and ultra-high pressure rocks: Implications for element transfer in subduction zones

High-pressure (HP) and ultra-high pressure (UHP) terranes are excellent natural laboratories to study subduction-zone processes. In this paper we give a brief theoretical background and we review experimental data and observations in natural rocks that constrain the nature and composition of the fluid phase present in HP and UHP rocks. We argue that a fluid buffered by a solid residue is compositionally well defined and is either an aqueous fluid (total amount of dissolved solids < 30 wt.%) or a hydrous melt (H 2O < 35 wt.%). There is only a small temperature range of approximately 50–100 °C, where transitional solute-rich fluids exist. A review of available experimental data suggest that in felsic rocks the second critical endpoint is situated at 25–35 kbar and ∼ 700 °C and hence must be considered in the study of UHP rocks. Despite this, the nature of the fluid phase can be constrained by relating the peak metamorphic conditions of rocks to the position of the wet solidus even if the peak pressure exceeds the pressure where the wet solidus terminates at the second critical endpoint. Transitional solute-rich fluids are expected in UHP terrains ( P > 30 kbar) with peak temperatures of about 700 ± 50 °C. At higher temperatures, hydrous granitic melts occur whereas at lower temperatures aqueous fluids coexists with eclogite-facies minerals. This argument is complemented by evidence on the nature of the fluid phase from high-pressure terrains. We show that in the diamond-bearing, high-temperature UHP rocks from the Kokchetav Massif there are not only hydrous felsic melts, but probably also carbonate and sulfide melts present. Hydrous quartzo-feldspathic melts are mainly produced in high temperature UHP rocks and their composition is relatively well constrained from experiments and natural rocks. In contrast, constraining the composition of aqueous fluids is more problematic. The combined evidence from experiments and natural rocks indicates that aqueous fluids liberated at the blueschist to eclogite facies transition are dilute. They contain only moderate amounts of LILE, Sr and Pb and do not transport significant amounts of key trace elements such as LREE, U and Th. This indicates that there is a decoupling of water and trace element release in subducted oceanic crust and that aqueous fluids are unable to enrich the mantle wedge significantly. Instead we propose that fluid-present melting in the sediments on top of the slab is required to transfer significant amounts of trace elements from the slab to the mantle wedge. For such a process to be efficient, top slab temperature must be at least 700–750 °C at sub-arc depth. Slab melting is likely to be triggered by fluids that derive from dehydration of mafic and ultramafic rocks in colder (deeper) portions of the slab.

English

Stillwater Mining Company produces platinum and palladium ore from a 1-to-3 meter wide zone, referred to operationally as the J-M reef, within a layered ultramafic- to-mafic cumulate intrusive deposit at Nye, Montana. The braggite and cooperite (Pt, Pd, Ni)xSy ore minerals occur in association with the sulfide minerals chalcopyrite (CuFeS2), pyrrhotite (Fe1-xS), pentlandite(Fe,Ni)9S8, and minor pyrite (FeS2), so that sulfide-bearing rock is for the most part mined as ore. Sulfide minerals posing a risk of acid generation occur almost exclusively in the ore zone, so that little risk associated with waste rock and underground workings was anticipated when the mine was originally permitted in the 1980's. This conclusion is being revisited through an operational validation program underway at the Stillwater Mine, which seeks to evaluate the baseline conclusion that ARD potential is low in mine waste materials. Samples from the gabbro (n= 15), norite (n= 16), anorthosite (n= 9), and troctolite (n=6) lithologies, identified through careful geological characterization, have been studied for whole rock geochemistry and acid generation potential. Results of this work do not support further assessment of acid drainage risk using kinetic test methods. Composites have been developed from these samples for studies of trace element release potential by lithology using the meteoric water mobility procedure. The data confirm the original baseline conclusion of low risk to water resources, which has also been substantiated through monitoring in surface and groundwater at the mine site. A limited number of confirmation samples will be collected in future operations.

Adsorption of trace elements from poultry litter by montmorillonite clay

Poultry litter (PL) is used as fertilizer on agricultural lands because of its high nutrient content. However, the litter also contains trace elements such as As, Cd, Cu, Pb, and Zn. On land application of PL, these trace elements may be absorbed by crops, leach into groundwater, or enter the aquatic system as run-off. The objective of this research was to study the effect of the addition of montmorillonite clay-mineral (CM) in reducing the release of trace elements from PL. Cd, Cu, and Zn showed significant decreases of 29, 34, and 22%, respectively, in PL aqueous leachate (compared with the control-PL without CM) on mixing with 0.05 g CM but no change in As, Co, and Cr concentrations was observed. Lead showed a significant increase in PL aqueous leachate on mixing with 0.2 g CM but Pb concentration was two orders of magnitude less than in CM aqueous leachate alone. On washing, the settled precipitate (PL + CM) in the centrifuge tubes with water (desorption study) most of the adsorbed metals (Cd 85%, Cu 61%, and Zn 100%) were released. The results of this study show that the addition of CM resulted in significant adsorption of Cd and Cu from PL.

Trace metals distributions in coastal sea ice of Terra Nova Bay, Ross Sea, Antarctica

In an attempt to clarify the release of trace elements from the seasonal coastal sea ice, samples were periodically collected in a nearshore station inside the Gerlache Inlet (Terra Nova Bay, Western Ross Sea), during the summer 2000/01 and analysed for dissolved and particulate cadmium, copper, iron, manganese and lead, as well as salinity, suspended particulate matter, nutrients and phytoplankton pigments. In order to provide insight on the metal association with the particles included in the sea ice, the metal solid speciation was also investigated. Both vertical distributions within the ice cores and temporal variations at the seawater interface were studied, in an effort to fully characterize the system and correlation among the considered parameters. Concentrations and speciation patterns clearly indicate metal incorporation within the annual sea ice due to resuspension of sediments, followed by release of particulate metals during melting as a primary process affecting trace metal availability in the Antarctic coastal waters.

Development of nitrogen-containing nickel-free austenitic stainless steels for metallic biomaterials—review

Metallic biomaterials—such as 316L stainless steel and cobalt-based alloys—have been used as biomaterials mainly because of their excellent mechanical and corrosion properties. However, the release of nickel trace elements—which cause toxicity—has prompted the development of nitrogen-containing nickel-free austenitic stainless steels. This paper reviews their development, traces the history of 316L stainless steel, and the improvement of properties by nitrogen addition. These steels are now available for production of implant devices such as bone plates and screws. Such production requires special techniques with nitrogen absorption treatment.

Decoupling of fluid and trace element release in subducting slab? Comment on “Redistribution of trace elements during prograde metamorphism from lawsonite blueschist to eclogite facies; implications for deep subduction-zone processes” by C. Spandler et al. (Contrib Mineral Petrol 146:205–222, 2003)

Decoupling of fluid and trace element release in subducting slab? Comment on “Redistribution of trace elements during prograde metamorphism from lawsonite blueschist to eclogite facies; implications for deep subduction-zone processes” by C. Spandler et al. (Contrib Mineral Petrol 146:205–222, 2003)

Microbial acidification and pH effects on trace element release from sewage sludge

Leaching of sludge-borne trace elements has been observed in experimental and field studies. The role of microbial processes in the mobilization of trace elements from wastewater sludge is poorly defined. Our objectives were to determine trace element mobilization from sludge subjected to treatments representing microbial acidification, direct chemical acidification and no acidification, and to determine the readsorption potential of mobilized elements using calcareous sand. Triplicate columns (10-cm diameter) for incubation and leaching of sludge had a top layer of digested dewatered sludge (either untreated, acidified with H 2SO 4, or limed with CaCO 3; all mixed with glass beads to prevent ponding) and a lower glass bead support bed. Glass beads in the sludge layer, support layer or both were replaced by calcareous sand in four treatments used for testing the readsorption potential of mobilized elements. Eight sequential 8-day incubation and leaching cycles were operated, each consisting of 7.6 d of incubation at 28 °C followed by 8 h of leaching with synthetic acid rain applied at 0.25 cm/h. Leachates were analyzed for trace elements, nitrate and pH, and sludge layer microbial respiration was measured. The largest trace element, nitrate and S losses occurred in treatments with the greatest pH depression and greatest microbial respiration rates. Cumulative leaching losses from both microbial acidification and direct acidification treatments were >90% of Zn and 64–80% of Cu and Ni. Preventing acidification with sludge layer lime or sand restricted leaching for all trace elements except Mo. Results suggested that the primary microbial role in the rapid leaching of trace elements was acidification, with results from direct acidification being nearly identical to microbial acidification. Microbial activity in the presence of materials that prevented acidification mobilized far lower concentrations of trace elements, with the exception of Mo. Trace elements mobilized by acidification were readsorbed by calcareous sand when present.

Trace element release from forest floor can be monitored by ion exchange resin tubes

AbstractRisk assessment of heavy metal input into forest ecosystems requires information about metal fluxes from the forest floor (organic layer) into the mineral soil. Common methods for the monitoring of element fluxes are generally time‐consuming and expensive. Additionally, the reliability of the results is in part contested especially for trace elements, showing very low concentrations which are sometimes even below analytical detection limit. We used ion exchange resin tubes installed below the forest floor to determine heavy metal and As fluxes at 25 forest monitoring sites in Germany. Chloride tracer experiments and the comparison of our data with throughfall and lysimeter data, determined within the Level II monitoring network, proved the accuracy of our method. Mean trace element fluxes based on the resin method were 50 g As ha–1 yr–1, 2 g Cd ha–1 yr–1, 168 g Cu ha–1 yr–1, 176 g Ni ha–1 yr–1, and 186 g Pb ha–1 yr–1.The results show that the organic layer may change into a source of heavy metals after emission has decreased.

Geochemical heterogeneity and element mobility in deeply subducted oceanic crust; insights from high-pressure mafic rocks from New Caledonia

Bulk-rock major and trace element geochemistry of a range of eclogite, garnet blueschist and garnet amphibolite rocks from northern New Caledonia has been determined in order to geochemically characterise subducted oceanic crust. The rocks experienced peak metamorphic conditions of 1.9 GPa and 600 °C and represent excellent samples of oceanic crust that was subducted to depths of approximately 60 km. The rocks can be divided into seven rock types that respectively have geochemical characteristics of enriched and normal mid-ocean ridge basalt, back-arc basin basalt, alkaline basalt, plagioclase-rich cumulate, seafloor-altered basalt and Fe–Ti basalt. All of the samples studied represent a single slice of oceanic crust interpreted to have formed in a back-arc or marginal basin setting. Examination of modern oceanic crust suggests that most subducting crust also contains a diverse range of mafic rock-types. The presence of minor amounts of alkaline and seafloor-altered basalts in the slab can greatly influence the recycling of incompatible elements and the depth of fluid release during subduction. Comparison of the high-grade metamorphic rocks with equivalent igneous rocks from western New Caledonia demonstrates that the main chemical variations of the rocks are related to differences in their magmatic history and to different degrees of seafloor alteration, whereas high-pressure metamorphism produced only minor changes. There is evidence for some depletion of LILE and B during subduction in a few of the analysed samples. However, most of the blueschists and eclogites with protoliths showing high LILE contents such as the back-arc basin and alkaline basalts still contain high LILE contents of 10–100 times the amount found in normal mid ocean ridge basalts. Therefore, even fluid mobile elements (B, LILE) may be efficiently subducted to sub-arc depths. Trace elements are most likely to be removed from the slab in regions of elevated temperature or in zones of intense fluid–rock interaction or partial melting. In contrast to the trace elements, large volumes of fluid are liberated from mafic rocks prior to eclogite-facies metamorphism, providing evidence for a decoupling of fluid and trace element release in subducted oceanic crust.